Chemical Composition with Respect to Particle Size

Distribution of Chemical Composition with Respect to Particle Size 

There are instruments capable of measuring the composition of individual particles (Chapter 6)t and eventually it will be possible to determine the size-composition p.d.f. Currently, such measurements are made on a research basis in practice the average composition of the particles in a discrete size interval is determined by collecting an aerosol sample over a period of several hours using a cascade impactor (Chapter 6) and analyzing the material on each stage chemically. The concentration measured in this way is related to g(u, wj,. rt. r, f) as follows  

These results illustrate that emissions from combustion facilities tend to be enhanced in certain elements, some toxic, relative to the original composition of the feed. This has been documented both for emissions from incineracors and for coal cuinbusiiuii (Table 1.2). It probably holds for smelting and other high-tetnperature processes involving multicomponent feedstocks. 

Elements in Airborne Coal Flyash Particles That Show Pronounced Concentration Trends with Respect to Particle Size (Davison et al., 1974) 

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Chemical Composition Aerosol composition measurements have most frequently been made with little or no size resolution, most often by analysis of filter samples of the aggregate aerosol. Sample fractionation into coarse and fine fractions is achieved with a variety of dichotomous samplers. These instruments spread the collected sample over a relatively large area on a filter that can be analyzed directly or after extraction Time resolution is determined by the sample flow rate and the detection limits of the analytical techniques, but sampling times less than 1 h are rarely used even when the analytical techniques would permit them. These longer times are the result of experiment design rather than feasibility. Measurements of the distribution of chemical composition with respect to particle size have, until recently, been limited to particles larger than a few tenths of a micrometer in diameter and relatively low time resolution. One of the primary tools for composition-size distribution measurements is the cascade impactor. 

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